Farmery A D, Hahn C E
Nuffield Department of Anaesthetics, University of Oxford, Radcliffe Infirmary, Oxford OX2 6HE, United Kingdom.
J Appl Physiol (1985). 2001 Apr;90(4):1282-90. doi: 10.1152/jappl.2001.90.4.1282.
The use of sidestream infrared and paramagnetic clinical gas analyzers is widespread in anesthesiology and respiratory medicine. For most clinical applications, these instruments are entirely satisfactory. However, their ability to measure breath-by-breath volumetric gas fluxes, as required for measurement of airway dead space, oxygen uptake, and so on, is usually inferior to that of the mass spectrometer, and this is thought to be due, in part, to their slower response times. We describe how volumetric gas analysis with the Datex Ultima analyzer, although reasonably accurate for spontaneous ventilation, gives very inaccurate results in conditions of positive-pressure ventilation. We show that this problem is a property of the gas sampling system rather than the technique of gas analysis itself. We examine the source of this error and describe how cyclic changes in airway pressure result in variations in the flow rate of the gas within the sampling catheter. This results in the phenomenon of "time distortion," and the resultant gas concentration signal becomes a nonlinear time series. This corrupted signal cannot be aligned or integrated with the measured flow signal. We describe a method to correct for this effect. With the use of this method, measurements required for breath-by-breath gas-exchange models can be made easily and reliably in the clinical setting.
旁流红外和顺磁临床气体分析仪在麻醉学和呼吸医学中应用广泛。对于大多数临床应用而言，这些仪器完全令人满意。然而，它们测量逐次呼吸的容积气体通量的能力，如测量气道死腔、氧摄取等所需的能力，通常不如质谱仪，这被认为部分是由于它们的响应时间较慢。我们描述了尽管Datex Ultima分析仪进行容积气体分析在自主通气时相当准确，但在正压通气条件下会给出非常不准确的结果。我们表明这个问题是气体采样系统的特性，而非气体分析技术本身的问题。我们研究了这个误差的来源，并描述了气道压力的周期性变化如何导致采样导管内气体流速的变化。这导致了“时间失真”现象，并且由此产生的气体浓度信号变成了一个非线性时间序列。这个被破坏的信号无法与测量的流量信号对齐或整合。我们描述了一种校正这种影响的方法。使用这种方法，可以在临床环境中轻松且可靠地进行逐次呼吸气体交换模型所需的测量。
